Fuel compositions for spark ignition engines



United States Patent O FUEL COMPOSITIONS FOR SPARK IGNITION ENGINES James L. Lauer, Philadelphia, Pa., assignor to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey No. Drawing. Application March 6, 1957 Serial N 0.. 644,222

3; Claims. or. 44-59 This invention relates to novel fuel compositions which substantially reduce the problem of spark plug fouling in-spark ignitioninternal combustion engines. The fuel compositions of the invention. contain novel additives decomposes to form deposits which are known to remainin. the combustion chamber as deposits on the walls and on the spark plug ceramic. Such deposits either conduct electricity, or are converted under combustion chamber conditions to products which conduct electricity. A build-up of such deposits on spark plugs provides an alternate path for the flow of electrical current. The resulting current leakage between spark plug terminals reduces the spark potential andeventually causes the plug to misfire. This phenomenon is known in the art as spark plug fouling. Many materials have been tested to determine their effectiveness, as fuel additives, in reducing spark plug fouling, but only limited success has been obtained.

An object of this invention is to provide novel fuel compositions for spark ignitionengines. A specific object is to provide novel fuel compositions which, when employed in a spark ignition internal combustion engine, effectively and substantially reduce the fouling of spark plugs. Another object of the invention is to provide a process for operating an engine in which the tendency toward fouling of the spark plugs is substantially reduced.

It hasnow been discovered that spark plug fouling can be substantially reduced by incorporating in fuel for a spark ignition engine a minor amount of an ester formed by reacting naphthenic acids with certain monohydric alcohols. Monohydric alcohols. which can be used to prepare the naphthenate esters in the fuel cornpositions of the present invention are cyclopentanols, cyclohexanols, phenylcarbinols, phenylethyl alcohols, phenylpropyl alcohols and thienylcarbinol.

The novel gasoline compositions of the present invention comprise mainly mixtures of petroleum hydrocarbons boiling in the range of from about 80 F. to 440 F., and usually from about 90 F. to 400 F. The gasoline compositions of the invention also contain, in addition to the additives of this invention, an anti-knock amount of an organo-metallic anti-knock agent such as tetraethyl lead, iron carbonyl, bis-cyclopentadienyl iron, and the like. Tetraethyl lead is the most commonly used organo-lead anti-knock additive, although other lead compounds such as tetramethyl lead, tetraphenyl lead, triethyltnethyl lead, and the like have been described as 2,918,360 Patented Dec. 22, 1 959 2,; useful. These lead anti-knock agents areused-i in amounts in the range of from about 0.1 to 6.0 cc;/g allon of gasoline. Other commonly usedgasoline addi-* tives can be present, suchas scavengers-for theorganometallic compound, anti-icing agents, detergents otheranti-knock agents, and the like.

In practicing the present invention, the sparkplug; anti-fouling additive is incorporated in the gasoline in" a minor amount sufficient to substantially reduce spark plug fouling in a spark ignition internal combustion engine. The addition of from about: 0.1 to5.0 cc;/gallon of gasoline, and preferably fromabout 0.5 to-l.0- cox/ gallon of gasoline, of the additive gives good'results. On? occasion, however, amounts of the additive outsideof? the above cited ranges can advantageously be'used? The spark pluganti-fouling additives ofthe-presentt invention are naphthenate esters of a monohydric alcohol. The monohydric alcohol can becyclopentanol, a cyclohexanol, a phenylcarbinol; a phenylethyl' alcohol, a phenylpropyl alcohol or thienyl carbinol. Theesters can be derived from any of the well known alcohols withinthe defined group. With the exception of thienyl carbinol, the alcohol can havealkyl substituents attached to nuclear carbon atoms. Preferably not more than 3 such substituents, each containing from.l to about 4 carbon atoms, are present; Cyclopenta-nol, cyclohexanol, phenylcarbinols, phenylethyl alcohols and* phen ylpropyl alcohols are well known and are preferably used. Thienyl carbinol (thienyl methyl alcohol)", which can. be prepared in accordance-with amethod given in- Berichte, volume 19, page 636, also gives goodresults.

The naphthenic acids used in preparing the naplithenate esters of the present invention are normally obtained from petroleum. Petroleum naphthenic acids are complex mixtures of alkyl-substituted, cycloparaflin-ic, monocarboxylic acids which occur in small'amounts as natural constituents of crude petroleum and fractions thereof. The naphthenic acids from which the additivesof the present invention are derived are preferably thoserecovered from the lubricating oiland gas oilfractions; of petroleum which boil within the range offrom-about 500 F. to about 1000 F; at atmospheric pressure; The acids from a fraction boiling within this range normal 1y contain from about 8 to about 30 carbon atoms-per molecule, and distill in the range-1 of-tfrom about 250 F. to about 600 F. at 2 mm. of mercury absolute pressure. Such acids can range in saponificationvalue-from about 50 to about 300 mgs. of KOH/gram on an un: saponifiablesfree. basis. In the practice of this.inven-. tion, esters derived from mixtures of such. acids. having an average saponification value of -485 mgs. of KOH/gram are preferred, since excellent results. areob v tained therewith.

Methods of recovering naphthenic acids from petroleum fractions are Well known-inthe art. Generally, such methods comprise sapon-ifyingtlie desired fraction of petroleum to obtain a mixture. consisting. essentially of a major proportion of unsaponifiable material and a minor proportion of naphthenatesoaps, effectingeat least a partial separation between the soaps and um saponifiable material, and then acidifying the separated soaps to obtain the desired naphthenic acids fractions in relatively concentrated form.

Specific examples of naphthenate esters of monohydric alcohols which may be employed in practicing the present invention are: cyclopentyl naphthenates, butyl cyclopentyl naphthenates, dipropyl cyclopentyl naphthenates, trimethyl cyclopentyl naphthenates; cyclohexyl naphthenates, propyl cyclohexyl naphthenates, dimethyl cyclohexyl naphthenates, triethyl cyclohexyl naphthenates; butylbenzyl naphthenates, trimethylbenzyl naphthenates, dipropylbenzyl naphthenates; diphenylmethyl naphthenates, triphenylmethyl naphthenates; alpha-phenylethyl naphthenates, beta-phenylethyl naphthenates; gamma-phenylpropyl naphthenates; thienyl methyl naphthenates; and homologues and isomers thereof.

. The naphthenate esters constituting the anti-fouling additives'of this invention can be prepared from the acids and monohydric alcohol by any of the methods commonly known in the art. Generally, the esterification of naphthenic acids with an alcohol can be carried out by heating and stirring the acids with excess alcohol in the presence of a catalyst such as para-toluene sul fonic acid, concentrated sulfuric acid or dry hydrogen chloride. It is not essential to esterification that the naphthenic acids be substantially free from unsaponifiable material, and acids containing up to about 20% by weight of unsaponifiable material can advantageously be employed. A lower unsaponifiables content is preferred, however, such as below 10% by weight, quantities of from about 3% to 8% by Weight giving excellent results.

In order to illustrate the spark plug anti-fouling effectiveness of the novel compositions of the present invention, methyl cyclohexyl naphthenates were prepared by esterification of methyl cyclohexanol with a petroleum naphthenic acid fraction. The alcohol employed was a commercially available mixture of the ortho, meta and para isomers having a boiling range of from 155 F. to 180 F., a refractive index (n of 1.461 and a specific gravity 15 C./ 15 C.) of 0.924. The naphthenic acids used, also commercially available, were recovered from a gas oil-lubricating oil fraction of petroleum. The acids contained 5.6 weight percent of unsaponifiable matter and had a distillation range, at 2 mm. of mercury absolute pressure, of from 315 F. to 485 F. Their average saponification value was 183 mgs. of KOH/gram which corresponds to an average molecular weight of naphthenic acids of 297, and to an average of about 19 carbon atoms per molecule. The above described acids were mixed with an excess of the alcohol in the presence of a small amount of para-toluene sulfonic acid as catalyst, and refluxed with stirring for about 3 hours at approximately 165-170 F. The resulting reaction products were washed with water containing dissolved Na CO to remove the catalyst, and diluted with a low boiling organic solvent. Methyl cyclohexyl naphthenates were recovered in relatively concentrated form by flashing off the water and organic solvent. Physical properties of the ester were as follows:

Specific gravity (15 C./ 15

Viscosity 100 F 200.4 SSU.

Viscosity 210 F 43.36 SSU.

Refractive index (.n 1.4885:0.0005.

Acid number 7.46 mgs. KOH per Saponification value 110.9 mgs. KOH per The spark plug anti-fouling effectiveness of the above prepared ester was demonstrated in a single-cylinder engine having a hemispherical combustion chamber, an overhead valve and a compression ratio of 11:1. This engine was operated on a highly aromatic, high octane, leaded gasoline fuel and a W30 mineral oil lubricant.

The engine was designed to stop when the spark plug misfires or shorts. The time of operation before such an engine stops is therefore a measure of the severity of spark plug fouling. The engine when employing the above fuel without the anti-fouling additive stopped after hours of operation. When the engine was operated on the same fuel containing 1 ml./gallon of the methyl cyclohexyl naphthenate additive prepared as above described, it operated for hours before stopping. This increase in time of operation is indicative of a significant and substantial reduction in spark plug fouling.

When the above procedure is repeated using cyclopentyl naphthenates, benzyl naphthenates, thienyl methyl naphthenates, other esters as above described, or mixtures of such esters, as the spark plug anti-fouling fuel additive, substantially equivalent results are obtained.

The exact mechanism by which the novel fuel compositions of this invention reduce the tendency toward fouling of the spark plugs is not definitely known. It is known, as above described, that the incorporation of small amounts of naphthenate esters of certain monohydric alcohols in a fuel for a spark ignition engine reduces spark plug fouling to a remarkable extent.

The invention claimed is:

1. A spark ignition internal combustion engine fuel composition consisting essentially of a major proportion of a mixture of petroleum hydrocarbons boiling in the gasoline range, an anti-knock amount of an organolead anti-knock additive and a minor amount, sufiicient to substantially reduce spark plug fouling, of a petroleum naphthenate ester of a monohydric alcohol, said monohydric alcohol being selected from the group consisting of cyclopentanol, cyclohexanol, phenylcarbinol, phenylethyl alcohol, phenylpropyl alcohol and thienyl v carbinol.

4. Composition according to claim 1 wherein the monohydric alcohol is phenylcarbinol.

5. Composition according to claim 1 wherein the monohydric alcohol is phenylethyl alcohol.

6. Composition according to claim 1 wherein the monohydric alcohol is thienyl carbinol.

7. Composition according to claim 1 wherein said organo-lead anti-knock additive is tetraethyl lead.

8. A spark ignition internal combustion engine fuel composition consisting essentially of a major proportion of gasoline, an anti-knock amount of an organolead anti-knock additive and from about 0.1 ml. to 5.0 mls. per gallon of gasoline of petroleum naphthenate esters of a monohydric alcohol selected from the group consisting of cyclopentanol, cyclohexanol, phenylcarbinol, phenylethyl alcohol, phenylpropyl alcohol, and thienyl carbinol.

References Cited in the file of this patent UNITED STATES PATENTS 1,841,254 Rosenbaum Jan. 12, 1932 2,316,754 Backoff et a1. Apr. 20, 1943 2,765,220 Yust Oct. 2, 1956 

1. A SPARK IGNITION INTERNAL COMBUSTION ENGINE FUEL COMPOSITION CONSISTING ESSENTIALLY OF A MAJOR PROPORTION OF A MIXTURE OF PETROLEUM HYDROCARBONS BOILING IN THE GASOLINE RANGE, AN ANTI-KNOCK AMOUNT OF AN ORGANOLEAD ANTI-KNOCK ADDITIVE AND A MINOR AMOUNT, SUFFICIENT TO SUBSTANTIALLY REDUCE SPARK PLUG FOULING, OF A PETROLEUM NAHTHENATE ESTER OF A MONOHYDRIC ALCOHOL, SAID MONOHYDRIC ALCHOL BEING SELECTED FROM THE GROUP CONSISTING OF CYCLOPENTANOL, CYCLOHEXANOL, PHENYLCARBINOL, PHENYLETHYL ALCOHOL, PHENYLPROPYL ALCOHOL AND THIENYL CARBINOL. 